Press & release modifier via SendKeys

I'm using the API function SendInput to send keystrokes to another app, but sometime for unknown reason when i try to release modifier(s), they won't and stay pressed even if i repeat the code many times.

I want to try using the class SendKeys.SendWait method but i cannot figure out how to use it for just releasing modifier(s), i tried
but it hold down Ctrl. There must be some char comes after ^ to release Ctrl, but i don't want to send anything, i tried SendKeys.SendWait("^^") but it cause error.